So I've been trying to figure out what kind of rear end ratio to get my 65 c10. I know some members has stated they're running 3.08 however I have a rather steep incline on the way to work. Even my 2000 monte carlo ss has to stay in 3rd to make it up the hill and it makes about 200hp stock versus my c10's 230 which supposedly make 140hp. I would like to go out and find a T5 but I doubt I could even use 4th or 5th on the hill climb to work. what do you guys think I should do for gearing?

Easy to find out. Should be a tag on rear end. Another option is to jack the truck up and turn one wheel and count the revolutions of the pinion. If it does about 3, then you have a 3.07 more than likely. If it goes almost 4, then you have a 3.73.

I would suspect if you have a 3speed trans you probably have the 3.07 gear ratio.

If you want to run a 5 speed, it would serve you best with a 3.73:1 rear gear.

I bet with the t5 you won't need to swap the rear end. I have a 5 speed in my C20 stock 4:56 rear, 1st is super low and 5th spins about 2600 @80mph. In my Apache I have stock 3:90 rear and 700r4 and it also does great in town or on the freeway. See what rear you have, a 3:73 is going to be a great all around gear. Keep in mind your tire size will affect everything as well. You can Google, tire, rear end, rpm, mph calculator and see the difference.

I have a T5 with the 0.72 overdrive gear, a 230ci engine, and a 3.73 rear diff. in my 1965 short bed. It drives just fine and the highway RPMs are in the 2100 range. I have 235/75R15 tires which are 28.8" tall.

If you swap to a 3.08 rear I think you will be pretty happy. Then I f you decide later to install a T5, the best option would be to find one with a 0.86 overdrive to match the 3.08. . If you go straight for the T5 swap, then get one with the 0.72 overdrive gear to match up well with a 3.73 or 3.90 rear. The 3.42 rear will tend to bog the 230ci if you have a 0.72.